[PATCH] powerpc/64: Use tick accounting by default

Christophe LEROY christophe.leroy at c-s.fr
Mon May 22 17:26:14 AEST 2017



Le 19/05/2017 à 16:41, Anton Blanchard a écrit :
> From: Anton Blanchard <anton at samba.org>
>
> ppc64 is the only architecture that turns on VIRT_CPU_ACCOUNTING_NATIVE
> by default. The overhead of this option is extremely high - a context
> switch microbenchmark using sched_yield() is almost 20% slower.
>
> To get finer grained user/hardirq/softirq statitics, the
> IRQ_TIME_ACCOUNTING option can be used instead, which has much lower
> overhead.

Does IRQ_TIME_ACCOUNTING allow the same granularity as 
VIRT_CPU_ACCOUNTING_NATIVE ?
I've quickly looked into the source, it seems that this option still 
accounts based on time ticks.
On a hardware doing mainly VoIP handling, the processes run a few ms 
every 20 ms. With TICK_CPU_ACCOUNTING and a 10ms tick, the processes 
either appear with 50% CPU or almost 0%.
Would it be more precise with IRQ_TIME_ACCOUNTING ?

Christophe

>
> As such, disable this option by default. If a user really wants it,
> they can still enable it manually.
>
> Signed-off-by: Anton Blanchard <anton at samba.org>
> ---
>  init/Kconfig | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/init/Kconfig b/init/Kconfig
> index 1d3475fc9496..a5c30acc1ede 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -342,8 +342,7 @@ config VIRT_CPU_ACCOUNTING
>
>  choice
>  	prompt "Cputime accounting"
> -	default TICK_CPU_ACCOUNTING if !PPC64
> -	default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
> +	default TICK_CPU_ACCOUNTING
>
>  # Kind of a stub config for the pure tick based cputime accounting
>  config TICK_CPU_ACCOUNTING
>


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